Heterotopic Ossification in Rectal Carcinoma: Report of a Case and Review of the Literature.

Heterotopic ossification in colorectal carcinoma is extremely rare. This report presents the case of a 57-year-old male who had undergone a low anterior resection following a diagnosis of rectal carcinoma. Histological examination showed heterotopic ossification in the tumor. The patient was referred to Ibaraki Medical Center, Tokyo Medical University, with a diagnosis of rectal carcinoma by a local physician. Abdominal computed tomography revealed thickening of the rectal wall with calcified deposits, and virtual colonoscopy showed stenosis with a mass in the rectum. The patient underwent a low anterior resection and diverting ileostomy in May 2014. Histological examination of the excised tumor showed moderately differentiated adenocarcinoma and an infiltration of spindle cells with numerous foci of osteoid and ossification, with osteoblastic rimming in the stroma. Immunohistochemical analysis of these spindle cells and osteoblasts revealed negative staining for AE1/AE3, suggesting a reactive change. There was metastasis in 1 of the 12 lymph nodes, and the tumor was diagnosed as stage IIIB (T4a, N1a, M0) rectal carcinoma. The patient had an uneventful recovery and was followed up at our outpatient clinic. In conclusion, the malignant potential of heterotopic ossification in rectal carcinoma has not been determined. However, heterotopic ossification is induced by tumor progression in a microenvironment, suggesting a high tumor malignity. The patient should be carefully monitored after surgery in terms of improved patient outcome.